Method of manufacturing arm

ABSTRACT

While one end of a material ( 31 ) that has nearly the same diameter as that of a first connecting portion ( 15 ) is secured, pressure is applied to the portion between the middle and the other end of the material ( 31 ). A slender portion ( 32 ), which has nearly the same diameter as that of a buckle portion ( 18 ), is formed adjacent to said other end of the material ( 31 ), and a stepped portion ( 20 ) is formed adjacent to the slender portion ( 32 ). Thus, a first-stage unfinished body ( 33 ) is formed. By radially enlarging a part of the slender portion ( 32 ), i.e. the portion between the distal end and the portion to become a buckle portion ( 18 ), until the diameter of said part becomes nearly the same as the diameter of a second connecting portion ( 16 ), the portion to become the second connecting portion ( 16 ) isformed. Thus, an arm-to-be portion is formed, wherein the portion that has not been enlarged shall be formed into the buckle portion ( 18 ). With external threads ( 17 ) formed along the cylindrical outer surface of the expanded portion, formation of the arm ( 5 ) is completed. The invention enables the reliable formation of a buckle portion ( 18 ) having a given length, resulting in stable production of arms ( 5 ) having a uniform buckling strength. The invention enables the easy production of an arm ( 5 ) regardless of whether the two ends of the arm ( 5 ) have different diameters.

TECHNICAL FIELD

[0001] The present invention relates to a method of producing atube-shaped arm having a buckle portion and adapted to be connected toan adaptor portion and a connectable member.

BACKGROUND OF THE INVENTION

[0002] Various arms are known conventionally, including a suspension armof an automobile and a tie rod of a steering mechanism. These armstypically have a tubular shape, with a ball joint attached to one end,and a cylindrical shaft supporting portion having a rubber bush attachedto the other end. There are various conventionally known examples of atubular-arm to which such a ball joint and a shaft supporting portionshall be connected with a given distance between the ball joint and theshaft supporting portion.

[0003] As is true with an arm disclosed in Japanese Patent ProvisionalPublication No. 1997-183385, these arms typically have a buckle portionfor protecting the other part of the arm by buckling when receiving anexternal load greater than a given value.

[0004] To be more specific, an arm disclosed in Japanese PatentProvisional Publication No. 1997-183385 is a part of a rack-and-pinionsteering mechanism and includes a shaft-supporting portion, a ball jointas a supporting portion, and an arm to be used as a tie rod. Theshaft-supporting portion has a cylindrical portion and external threads.A rubber bush to which a rack shaft as an adaptor portion will beattached is contained in the cylindrical portion. The ball joint isadapted to be attached to a knuckle member for supporting wheels. Theshaft-supporting portion and the ball joint are respectively connectedto the two opposing ends of the arm.

[0005] The arm is formed in a generally cylindrical shape and has afirst connecting portion at one end and a second connecting portion atthe other end. Internal threads to be engaged with the external threadsof the shaft-supporting portion are formed in the cylindrical innersurface of the first connecting portion. Internal threads to be engagedwith the external threads of the ball joint are formed in thecylindrical inner surface of the second connecting portion. A buckleportion which is smaller in diameter and adapted to buckle whenreceiving a load greater than a given value is provided at the axialmiddle of the arm. The arm is produced by using a material having thesame diameter as that of the first connecting portion and the secondconnecting portion. The buckle portion of the arm, which is smaller indiameter than the other part of the arm and has a hexagonal outer shape,is formed by applying pressure to the axial middle of the material fromthe outer surface towards the center of the material, while securingboth ends of the material.

[0006] As the buckle portion of the arm disclosed in Japanese PatentProvisional Publication No. 1997-183385 is formed by applying pressureto the axial middle of the material from the outer surface, there is thepossibility of parts of the first connecting portion and the secondconnecting portion, i.e. the parts adjacent to the buckle portion,becoming narrower together with the buckle portion, during the processof forming the buckle portion. This may prevent production of buckleportions having a given, uniform axial length, making it difficult toachieve a stable buckling strength. In other words, in order to enablethe production of buckle portions having a given, uniform axial length,it is necessary to prevent undesirable deformation of the parts of thefirst connecting portion and the second connecting portion adjacent tothe buckle portion by, for example, inserting insert dies or similarmembers into the first connecting portion and the second connectingportion so as to prevent reduction of the diameter of the parts of thefirst connecting portion and the second connecting portion adjacent tothe buckle portion. This, however, may complicate the production of thearm.

[0007] As its first connecting portion and second connecting portionhave nearly the same diameter, the conventional arm described abovecannot be connected to a shaft supporting portion and a ball joint thatare provided with external thread portions having different diameters.

[0008] In order to solve the above problem, an object of the presentinvention is to provide an arm production method which enables the easyand reliable production of an arm having a given, uniform bucklingstrength.

DISCLOSURE OF THE INVENTION

[0009] The present invention provides a method of producing an arm whichwill be connected to an adaptor portion and a connectable member andincludes a tubular first connecting portion provided at one end of thearm and adapted to be connected to said adaptor portion, a tubularsecond connecting portion provided at the other end of the arm andadapted to be connected to said connectable member, and a buckle portionwhich is smaller in diameter than the first connecting portion as wellas the second connecting portion and provided between the firstconnecting portion and the second connecting portion so as to bucklewhen a load greater than a given value is applied to the firstconnecting portion or the second connecting portion, said method callingfor forming an unfinished body by narrowing one end portion of a tubularmaterial that has a diameter corresponding to that of either one of thefirst connecting portion or the second connecting portion so as to formsaid one end portion into a small diameter portion having a diametercorresponding to that of said buckle portion, and radially enlarging theportion between the end of the slender portion of the unfinished bodyand the portion of the slender portion to be formed into the buckleportion so as to increase the diameter to correspond to the diameter ofthe other one of the first connecting portion or the second connectingportion, i.e. the connecting portion having a diameter different fromthat of the material. By forming an unfinished body by narrowing one endportion of a tubular material having a diameter corresponding to eitherone of the first connecting portion or the second connecting portion soas to form said one end portion into a small diameter portion having adiameter corresponding to that of said buckle portion, and radiallyenlarging the portion between the end of the slender portion of theunfinished body and the portion of the slender portion to be formed intothe buckle portion so as to increase the diameter to correspond to thediameter of the other one of the first connecting portion or the secondconnecting portion, the invention enables the reliable formation of abuckle portion having a given length and the stable production of armshaving a uniform buckling strength.

[0010] A method of producing an arm according to another feature of theinvention is characterized in that the first connecting portion and thesecond connecting portion have different diameters and that the methodcalls for use of a material having a diameter that corresponds to thegreater of the diameters of the first connecting portion and the secondconnecting portion. By using a material having a diameter thatcorresponds to that of the greater of the diameters of the firstconnecting portion and the second connecting portion, the arm is formedbased on the greater of the diameters of the two connecting portions.Therefore, the invention is effective in reducing the proportion bywhich the diameter of the slender portion of the unfinished body isincreased, thereby facilitating the production of the mold for radiallyenlarging the slender portion and consequently improving themanufacturability of the entire arm.

[0011] A method of producing an arm according to yet another feature ofthe invention is characterized in that a stepped portion having atubular shape with a diameter greater than the buckle portion is formedbetween the buckle portion and at least one of the two connectingportions, i.e. the first connecting portion and the second connectingportion, by narrowing the corresponding portion or portions of thematerial. By the feature described above, which calls for forming astepped portion having a tubular shape with a diameter greater than thebuckle portion between the buckle portion at least one of the twoconnecting portions, the invention enables the formation of a buckleport that is ensured to have a given buckling strength regardless ofwhether the diameter of the buckle portion is greatly different fromthat of the first connecting portion or the second connecting portion.

[0012] A method of producing an arm according to yet another feature ofthe invention is characterized in that the first connecting portion andthe second connecting portion have different diameters and that externalthreads to be engaged with either one of the adaptor portion or theconnectable member are formed along the cylindrical outer surface of theconnecting portion that has the smaller diameter. As external threads tobe engaged with either the adaptor portion or the connectable member areformed along the cylindrical outer surface of the connecting portionthat has the smaller diameter, the area of the threads to be formed issmall in comparison with a structure that calls for threading the largerconnecting portion. Therefore, the invention facilitates threadingoperation, thereby improving the manufacturability of the arm.

BRIEF DESCRIPTION OF THE DRAWINGS

[0013]FIG. 1 is a process drawing showing the process of producing anarm by an arm production method according to an embodiment of thepresent invention, wherein (a) is a side view of the material, (B) aside view of an unfinished body, and (C) a side view of the arm;

[0014]FIG. 2 is a side view of a connecting device provided with an armproduced by said arm production method; and

[0015]FIG. 3 is a side view of a connecting device provided with an armproduced by an arm production method according to another embodiment ofthe present invention.

PREFERRED EMBODIMENT OF THE INVENTION

[0016] Next, the configuration of an arm production method according toan embodiment of the present invention is explained hereunder, referringto the drawings.

[0017] Referring to FIG. 2, numeral 1 denotes a connecting device to beused in, for example, a suspension arm of an automobile.

[0018] The connecting device 1 has a pair of shaft-supporting portions2, 3 serving as adaptor portions. The connecting device 1 also has anarm 5 provided with a connector portion 4, which may be made of anadjusting tube or the like and serves as a connectable member. Theaforementioned shaft-supporting portion 3 is attached to an end of thearm 5, and the connector portion 4 is attached to the other end of thearm 5 in the state that the shaft-supporting portion 2 is attached tothe opposite end of the connector portion 4.

[0019] Each one of the two shaft-supporting portions 2,3 has acylindrical portion 7 made of metal. A rubber bush 8 is provided insideeach cylindrical portion 7. The rubber bush 8 may consist of an innercylinder and rubber bonded to the inner cylinder by vulcanization. Theshaft-supporting portion 2 is integrally provided with a cylindricalconnecting arm portion 10, which projects from the cylindrical outersurface of the cylindrical portion 7 in the direction parallel to thediameter of the cylindrical portion 7. External threads 11 are formedalong the cylindrical surface of the end portion of the connecting armportion 10.

[0020] The arm 5 is formed of a metal into a generally cylindrical shapeand provided, at one of its axial ends, with a cylindrical firstconnecting portion 15. The outer edge of the first connecting portion 15is welded or otherwise joined to the cylindrical outer surface of thecylindrical portion 7 of the shaft-supporting portion 3. A cylindricalsecond connecting portion 16 is formed at the other axial end of the arm5. The second connecting portion 16 extends coaxially with the firstconnecting portion 15. External threads 17 are formed along thecylindrical outer surface of the second connecting portion 16. Acylindrical buckle portion 18 is provided at the axial middle of the arm5 in such a way as to be coaxial with the first connecting portion 15and the second connecting portion 16. The outer diameter of the buckleportion 18 is smaller than that of the first connecting portion 15 aswell as that of the second connecting portion 16.

[0021] A stepped portion 20 is provided between the first connectingportion 15 and the buckle portion 18. The stepped portion 20 iscomprised of portions having different diameters, i.e. a firstfrusto-conical portion 21, a cylindrical small diameter portion 22, anda second frusto-conical portion 23. The first frusto-conical portion 21extends contiguously from the first connecting portion 15 and graduallynarrows towards the buckle portion 18. The small diameter portion 22extends from the end of the first frusto-conical portion 21 facingtowards the buckle portion 18 in such a way as to be coaxial with thefirst connecting portion 15. The second frusto-conical portion 23extends contiguously from the small diameter portion 22 to the buckleportion 18 and gradually narrows towards the buckle portion 18.

[0022] A third frusto-conical portion 25 is formed between the secondconnecting portion 16 and the buckle portion 18 in such a manner thatone end of the third frusto-conical portion 25 is contiguous with thesecond connecting portion 16 and that the other end of the thirdfrusto-conical portion 25 is contiguous with the buckle portion 18, withthe diameter of the third frusto-conical portion 25 gradually decreasingfrom the second connecting portion 16 towards the buckle portion 18.

[0023] The aforementioned connector portion 4 has a connector body 27,which is made of a metal and has a shape resembling a hexagonal donut. Apair of nuts 28,28 serving as positioning portions are respectivelydisposed at the two axial ends of the connector body 27. Internalthreads (not shown) to be meshingly engaged with the external threads 11of the connecting arm portion 10 of the shaft-supporting portion 2 areformed in the cylindrical inner surface of one end of the connector body27. Internal threads (not shown) are formed also in the cylindricalinner surface of the other end of the connector body 27 so that the arm5 can be connected to the connector body 27 with said internal threadsmeshingly engaged with the external threads 17 of the second connectingportion 16 of the arm 5. The nuts 28,28 are adapted to be respectivelyscrewed onto the external threads 11 of the connecting arm portion 10 ofthe shaft-supporting portion 2 and the external threads 17 of the secondconnecting portion 16 of the arm 5 and abut against the two axial endsof the connector body 27, thereby positioning the external threads 11 ofthe connecting arm portion 10 and the external threads 17 of the arm 5in such a state that the external threads 11,17 are prevented fromengaging with the internal threads of the connector body 27.

[0024] The edge of the first connecting portion 15 of the arm 5 isintegrally joined to the cylindrical outer surface of the cylindricalportion 7 of the shaft-supporting potion 3 by welding. Theshaft-supporting potion 2 is integrally connected to the connector body27 with the external threads 11 of the connecting arm portion 10 of theshaft-supporting portion 2 meshingly engaged with the internal threadsand the nut 28 that are disposed at one end of the connector body 27.The shaft-supporting potion 3, too, is integrally connected to theconnector body 27 with the external threads 17 of the second connectingportion 16 of the arm 5, to which the shaft-supporting potion 3 shall beconnected, meshingly engaged with the internal threads and the nut 28 atthe other end of the connector body 27. Thus, the connecting device 1 isformed, with the two shaft-supporting potions 2,3 connected through thearm 5 and the connector portion 4 so that there is a given distancebetween the respective centers of the two shaft-supporting potions 2,3.

[0025] Next, the process of producing said arm is explained hereunder,referring to the drawings.

[0026] First, as shown in FIG. 1(a), the present embodiment requires useof a material 31, which is formed by cutting to a given length acylindrical pipe (not shown) having nearly the same diameter as theouter diameter of the first connecting portion 15, which is the greaterof the two connection portions of the arm 5. In the state where one endof the material 31 is secured, pressure is applied in the inwardlyradial direction to the area from the middle part to the other end ofthe material 31 so that a stepped portion 20 and a slender portion 32,i.e. the small diameter portion having nearly the same diameter as thebuckle portion 18, are formed. As a result, a first-stage unfinishedbody 33, which is the unfinished body shown in FIG. 1(b) and has thefirst connecting portion 15 at one end, is formed by pressure formation.

[0027] The distal end portion of the slender portion 32 of thefirst-stage unfinished body 33 is radially enlarged until its outerdiameter becomes nearly equal to that of the second connecting portion16 of the arm 5, while the base end of the slender portion 32, i.e. theportion that is adjacent to the stepped portion 20 and sahll be formedinto the buckle portion 18, remains unchanged. As a result, the portionwhich is not referred to in the drawing and shall become the secondconnecting portion is formed. Thus, an arm-to-be portion having aslender portion 32 is formed. The slender portion 32 at the base end,which was not enlarged, shall be formed into the buckle portion 18later.

[0028] Thereafter, the second connecting portion 16 is completed, withthe external threads 17 formed along the cylindrical outer surface ofthe aforementioned portion to become the second connecting portion.Thus, formation of the arm 5 shown in FIG. 1(c) is completed.

[0029] As described above, a material 31 having an outer diametercorresponding to the outer diameter of the first connecting portion 15,which is the greater of the two connecting portions, is used to form anarm 5. The process of forming the arm 5 is comprised of steps ofnarrowing one end of the material 31 to form the slender portion 32having a diameter corresponding to the outer diameter of the buckleportion 18, and radially enlarging the distal end portion of the slenderportion 32, i.e. the portion between the distal end and the portion tobe formed into the buckle portion 18, until the outer diameter of saiddistal end portion becomes nearly equal to that of the second connectingportion 16. The process described above ensures reliable formation of abuckle portion 18 having a given length, resulting in stable productionof arms 5 having a uniform buckling strength.

[0030] Furthermore, as the embodiment enables the easy production of anarm 5 regardless of whether the first connecting portion 15 at one endof the arm 5 and the second connecting portion 16 at the other end ofthe arm 5 have different diameters, the embodiment is applicable to awide range of usage.

[0031] Another benefit of the embodiment lies in use of a material 31having an outer diameter corresponding to the outer diameter of thefirst connecting portion 15, which is the greater of the two connectingportions of the arm 5; the use of such a material 31 reduces theproportion by which the diameter of the slender portion 32 of theunfinished body 33 is increased, thereby facilitating the production ofthe mold for radially enlarging the slender portion 32 and consequentlyimproving the manufacturability of the entire arm.

[0032] The first connecting portion 15, which is the greater of the twoconnecting portions of the arm 5, is welded to the shaft-supportingpotion 3. By means of the external threads 17 formed along thecylindrical outer surface, the second connecting portion 16, which isnarrower than the first connecting portion 15, is connected to theconnector portion 4 to which the shaft-supporting potion 2 is attached.Thorough welding of the first connecting portion 15, which is thegreater of the two connecting portions of the arm 5, ensures that thearm 5 is firmly connected to the shaft-supporting potion 3. As thediameter of the second connecting portion 16 is smaller than that of thefirst connecting portion 15, the diameter of the connector portion 4,which is adapted to be screwed onto the external threads 17 of thesecond connecting portion 16, is also reduced. As a result, internalthreads to be formed in the connector portion 4, too, are reduced.Therefore, the embodiment not only improves the manufacturability of theconnector portion 4 but also facilitates reduction of the weight anddimensions of the connector portion 4.

[0033] The first connecting portion 15, the second connecting portion16, and the buckle portion 18 are coaxially provided. Therefore, theseportions have a nearly uniform wall thickness, even though they areformed by narrowing or radially enlarging the tubular material 31.Because of this feature, the embodiment provides an arm having stablecharacteristics: for example, the buckle portion 18 has a stable bendingstress against buckling, or the arm can be reliably connected to theshaft-supporting potions 2,3 at predetermined locations.

[0034] Furthermore, providing the stepped portion 20 adjacent to thefirst connecting portion 15 facilitates the formation of the buckleportion 18 by narrowing the corresponding portion of the material 31while preventing deformation of the other part of the material. Even incases where there is a large difference between the diameter of thebuckle portion 18 and the diameter of the first connecting portion 15,which is the greater of the two connecting portions of the arm 5, thebuckle portion that has the reliable ability of buckling under a load ofmore than a given value.

[0035] Although the invention is explained referring to the aboveembodiment, which may serve as a part of a suspension arm with theshaft-supporting potions 2,3 respectively connected to the two ends ofthe arm, the invention is applicable to an arm of any type, including atie rod 41 of a steering device shown in FIG. 3.

[0036] The connecting device 42 shown in FIG. 3 has the same structureas the embodiment shown in FIGS. 1 and 2, except that the connectorportion 4 to be connected to the shaft-supporting potion 2 is a balljoint 43, and that the other shaft-supporting potion, i.e. theshaft-supporting potion 3, is another ball joint 44. The ball joint 43has an arm portion 45 projecting therefrom. An external thread portion46 is formed along the cylindrical outer surface of the arm portion 45.The ball joint 44 has a ball stud 49, which includes a stud portion 48in the shape of a solid cylinder. According to the present embodiment,the arm is the tie rod 41 and constitutes a part of a steering device.The tie rod 41 has a first connecting portion 15 at one end thereof anda second connecting portion 16 at the other end. Formed in the internalsurface of the second connecting portion 16 of the tie rod 41 areinternal threads 50 to be engaged with the external thread portion 46 ofthe arm portion 45 of the ball joint 43. The stud portion 48 of the balljoint 44 is attached to the first connecting portion 15 of the tie rod41 by inserting the stud portion 48 into the first connecting portion 15and narrowing the first connecting portion 15 by pressure-clamping orany other appropriate means.

[0037] In addition to the connecting device 42 shown in FIG. 3 and theconnecting device 1 shown in FIGS. 1 and 2, the invention is applicableto any arm, provided that an adaptor portion and a connectable memberare connected to the arm with a given distance between the adaptorportion and the connectable member and that the arm includes a buckleportion 18 arranged to buckle when receiving a load of more than a givenvalue.

[0038] The embodiment shown in FIGS. 1 and 2 calls for connecting theshaft-supporting potion 2 to the arm 5 via the connector portion 4.However, the connecting arm portion 10 of the shaft-supporting portion 2may be provided with internal threads to be engaged with the externalthreads of the second connecting portion 16 of the arm 5 so that theconnecting arm portion 10 of the shaft-supporting portion 2 can bedirectly connected to the arm 5.

[0039] Although the embodiment shown in FIGS. 1 and 2 includes a steppedportion 20, the stepped portion 20 may be omitted. Or, in an alternativestructure, stepped portion 20 may be provided contiguous with the secondconnecting portion 16.

[0040] Possible Industrial Application

[0041] As described above, an arm production method according to theinvention is applicable to producing an arm that may be used for asuspension arm of an automobile or a tie rod of a steering mechanism.

1. An arm production method for producing a cylindrical arm which willbe connected to an adaptor portion and a connectable member andincludes: a tubular first connecting portion provided at one end of thearm and adapted to be connected to said adaptor portion, a tubularsecond connecting portion provided at the other end of the arm andadapted to be connected to said connectable member, and a buckle portionwhich is smaller in diameter than the first connecting portion as wellas the second connecting portion and provided between the firstconnecting portion and the second connecting portion so as to bucklewhen a load greater than a given value is applied to the firstconnecting portion or the second connecting portion, said methodcomprising steps of: forming an unfinished body by narrowing one endportion of a tubular material that has a diameter corresponding to thatof either one of the first connecting portion or the second connectingportion so as to form said one end portion into a small diameter portionhaving a diameter corresponding to that of said buckle portion, andradially enlarging the portion between the end of the slender portion ofthe unfinished body and the portion of the slender portion to be formedinto the buckle portion so as to increase the diameter to correspond tothe diameter of the other one of the first connecting portion or thesecond connecting portion.
 2. An arm production method as claimed inclaim 1, wherein: the first connecting portion and the second connectingportion have different diameters, and the arm production method callsfor use of a material having a diameter that corresponds to the greaterof the diameters of the first connecting portion and the secondconnecting portion.
 3. An arm production method as claimed in claim 1 orclaim 2, wherein: a stepped portion having a tubular shape with adiameter greater than the buckle portion is formed between the buckleportion and at least one of the two connecting portions, i.e. the firstconnecting portion and the second connecting portion, by narrowing thecorresponding portion or portions of the material.
 4. An arm productionmethod as claimed in any one of the claims from claim 1 to claim 3,wherein: the first connecting portion and the second connecting portionhave different diameters, and external threads to be engaged with eitherone of the adaptor portion or the connectable member are formed alongthe cylindrical outer surface of the connecting portion that has thesmaller diameter.